Replication of enhancer-deficient amphotropic murine leukemia virus in human fibrosarcoma but not in primary human fibroblasts

Amphotropic murine leukemia virus (MLV) replicates in cells from various mammalian species including humans and is a potential contaminant in MLV vector preparations for human gene transfer studies. In general, MLV replication depends on the expression of viral genes under the control of 75 bp enhancer elements in the long terminal repeat. However, in specific human fibrosarcoma and lymphoma lines replication of amphotropic MLV is possible without these enhancers. Fibrosarcomas are malignant tumors of fibroblast origin. To test the replication potential of intact and enhancerless amphotropic MLV in untransformed cells, infection studies with these viruses were carried out in three types of primary human fibroblasts. Replication of amphotropic MLV is observed in two of three tested fibroblast strains. None of these primary human fibroblasts is permissive for enhancer-deficient MLV, suggesting that replication of this virus may be limited to transformed cells.